Although environmental tobacco smoke (ETS) exposure is nearly universal, the effects of ETS on adults with asthma have not been well characterized. The present study has three broad objectives. First, to develop and validate a questionnaire instrument for measuring ETS exposure in adult asthmatics living in California. Second, to assess the prevalence of ETS exposure in adults with asthma. Third, to evaluate the impact of ETS exposure on asthma severity and other health outcomes. We would develop a questionnaire instrument to measure ETS exposure in a variety of settings and validate the instrument against a biomarker of ETS exposure. We would administer the instrument to an ongoing panel of adults with asthma, enabling us to assess the impact of ETS exposure on asthma severity, quality of life, health care utilization, and health care costs. Our proposed study would provide a clearer understanding of the effects of a common, potentially aggravating exposure on adults with asthma.